Manufacture of paper for photographic purposes



Patented Aug. 1924.

7 UNITED STATES EDUARD SGHLOEMANN', 0F DUREN, GERMANY.

MANUFACTURE OF PAPER FOR PHOTOGRAPHIC PURPOSES.

No Drawing. Application filed June 9,

To all whom it may concern Be it known that I, EDUARD ScHnonMANN,subject of the German Republic, residing at Duren, Rheinland, Germany,have invented certain new and useful Improvements in the Manufacture ofPaper for Photographic Purposes, of which the following is aspecification.

The invention relates .to improvements in the manufacture of paper forphotographic purposes. In order to make ordinary paper suitable for thepurposes of the photographic industries they are coated with asuspension of sulphate of barium (blanc fixe) in gelatine, glue,,caseinor similar binders. This coating serves a double purpose. On the onehand it prevents the infiltration of the photographic emulsion (bromideof silver gelatine) into the fibre of thepaper and on the other hand itprotects the photographic emulsion against the action of impuritiescontained in the paper, which owing to-their chemical action may have adisturbing effect upon the picture during the subsequent de velopment.

The treatment of the paper is carried out in the following manner.Pulverized heavy spar or precipitated sulphate of barium in the drystate or as a dough is mixed with a binding agent and this mixture isapplied to the chine.

This invention consists in bringing together Ba-ions. on the one handand SO,- ions on the other hand in theqpresence of a protective colloidand maturing the emulsion of sulphate of barium so produced in gelatine,preferably at higher temperatures, 111 011181 to obtain a certain sizeof grain. After this size of grain has been attained the maturingprocess is discontinued, the

- stiff mass is granulated, washed and after re-melting applied to theraw paper, the

protective colloid acting at the same time' as binding medium.

The improved process is distinguished from the old process described inthe preamble by the fact that by the employment of pure raw materials(for instance chloride of barium, chemically pure sulphate of ammoniaand purified gelatine as protective colloid) after Washing out thesulphate of barium gelatine and completely removing the products ofconversion a barium coating is obtained, which in regard to puritysatisfies the highest requirements and is therepaper by means of aspreading ma- 1923. Serial No. 644,488.

for of the greatest importance for the manufacture of highgradephotographic paper. By means of the improved process an easy andabsolutely uniform distribution of the sulphate of barium in the bindingagent is furthermore possible, as the sulphate of barium forms itself bythe admixture of two solutions in the binding agent acting as protective colloid. It is also of importance in the improved process thatowing to the matu'ring, the sulphate of barium may be produced in anysize of grain. The crude mechanical granulation of the heavy spa-r orthe precipitated sulphate of barium of the known process is replaced bythe far exacter operating colloid-chemical maturing process, in whichthe original concentration of the brine, the presenceof otherelectrolytes, the kind and concentration of the protective colloid, aswell as the time and the temperature are the factors, which are ofinfluence for the size of the grain to be obtained.

The following may serve as an example for the carrying out of theprocess: with a heated solution of 500 gr. chloride of barium in 10litres of 20% watery gelatine is mixed a solution of 300 gr. sulphate ofammonia in 2.5 litres of water and-the mixture is allowed to mature at araised tem erature I (approximately at 50 to 70) unti a certain size ofgrain is obtained. If no importance is attached to a coarse grain, thematuring stage may be omitted and an emulsion of colloidal distributedsulphate of barium in gelatine is obtained.

The emulsion is allowed to stiffen, is then granulated according to themethods customary in the photographic industries and washed until thewater produces no longer any chemical reaction upon the salts ofconversion.

The emulsion thus purified is melted and applied to the paper. To thismass may be added, as required, further quantities of gelatine or ofanother binding agent (glue,

paper for photographic purposes the production of a coating emulsion ofsulphate of paper for p otographic purposes the pro-- duction of acoating emulsion of sulphate of barium, which consists in bringingtogether Ba-ions and SO -ions in the presence of a protective colloid,allowing said emulsion of sulphate of barium to mature until a certainsize of grain is obtained, granulating the stiff mass, washing andre-melting it.

4. The process for the manufacture of paper for photographic purposes,which consists in coating raw paper with an emulsion of sulphate ofbarium in a binding 111E- dium, said emulsion being obtained by thesulphate of barium being produced in the binding medium by bringingtogether Ba ions and SO -ions.

5. The process for the manufacture of paper for photographic pur oses,which consists in mix'in a heated so ution of 500 gr..of chloride ofarium in 10 litres of 20% watery gelatine with a solution of 300 gr.sulphate of ammonia in 2.5 litres of water, allowin said emulsion ofcolloidal distributed sulphate of barium in gelatine to stiflen,granulating, washing, re-melting and applying it to the raw paper.

6. The process for the manufacture of paper for photographic purposeswhich consists in mixing a heated solution of chloride of barium 1nwatery gelatine with a solution of sulphate of ammonia in water,allowing said emulsion to mature at raised temperatures until a certainsize of grain is produced, cooling said emulsion until .it stiffens,granulatmg, washing, re-melting and applying it to the raw paper.

In testimony whereof I have signed my name to this specification.

EDUARD SCI-ILOEMANN.

